1. Field of the Invention
The present invention relates to an improved process for tableting fine powders. In one aspect, the invention relates to improving the cohesiveness of the fine powders, while in another aspect the invention relates to improving the flow properties of fine powders.
2. Description of the Art
Fine powders can and do cause several problems when being handled, particularly when being tableted. For example, such powders flow very poorly through chutes and channels of processing equipment, stick together and bridge across the die during the loading step of tableting, creep between the punch and die during the compression and ejection steps of tableting, form air pockets in the loaded die resulting in capping and present a dust hazard. These problems offer a potential for damage to the processing machinery and the physical integrity of the tablet.
Most conventional techniques for alleviating these problems employ mixing the fine powders with binding and lubricating agents. Binders improve the strength of the compacts while lubricants increase the transmission of forces when tableting and reduce sticking to machine surfaces. Both processing agents are generally incorporated into powders in the form of aqueous or organic solutions and range from graphite and stearic acid to gum and molasses solutions. Binders which are insoluble in aqueous solutions are usually dissolved in organic solvents and then added to the fine powder. For example, Tablet Making by Arthur Little and K. A. Mitchell, The Northern Publishing Co., Ltd., 1968 at pages 48 and 49 discloses dissolving insoluble binders in trichloroethylene or ethanol and then adding the solution to the fine powder prior to tableting.
U.S. Pat. No. 3,838,064 discloses a method for controlling dust in a normally high-dusting material by working the material with fribrillatable polytetrafluoroethylene.